1. Field
The present invention relates to a printed wiring board mounted with a ball grid array (BGA) package or the like and an information processing device incorporating the printed wiring board.
2. Description of the Related Art
Conventionally, a printed wiring board implemented in a portable notebook personal computer (hereinafter referred to as a note PC) has been reinforced differently and various measures have been taken against the peeling and disconnection of electrodes (pads) caused by stress (warp) due to an external shock and heat when the note PC is carried by a user.
A printed wiring board mounted with a ball grid array (BGA) package as shown in FIG. 8 is known. In this board, leads 51 are drawn out of the outermost pads of the BGA package at right angles to each side of the BGA package. The leads of the inner pads have a normal width and are routed in random directions. The surface leads of the inner pads are routed to pass between the outermost pads.
When an external force is applied in which direction the BGA package peels off the printed wiring board, it concentrates on the pads in the four corners of the board. The BAG package is therefore likely to start peeling off the four corners of the board. To prevent this, the pads in the four corners are increased in number and formed as reinforcing pads which expand outside the package or which are not angular but circular to increase in their resistance to peeling, as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2001-068594.
As lead-free materials are adopted for bumps (solder balls) in use for environmental protection, the solder balls decrease in viscosity. Therefore, the inner pads as well as the pads in the four corners of the board and their adjacent pads are peeled off or cracked by an external shock and thus electrically disconnected easily.
The BGA package increases in size in accordance with recent high degree of integration, whereas the solder balls (bumps) decrease in diameter and their pitches become narrow. In order to reduce a note PC in size and weight, the requirements to thin the printed wiring board and implement it at high density is increasing. Accordingly, the printed wiring board is warped and vibrated more easily and stress is applied to the BGA package mounted on the board more greatly than conventional.
In contrast, Jpn. Pat. Appln. KOKAI Publication No. 2000-261110 discloses a technique of drawing leads in radial directions from the center of a transformation portion within a board such that the board in its entirety can increase in bonding strength without increasing the size of electrode pads. Since the leads are drawn in the radial directions, the bonding strength is increased against a heat stress generated in the radial directions. However, the Publication No. 2000-261110 has to take into consideration a relationship in the actual wiring in the BGA package and the directions of the leads. It is very difficult to design the leads as disclosed in the Publication for each BGA package. Even though such leads can be achieved, they require time and effort and thus they are not cost-justified.